Heretofore, an in-vehicle battery including a thin heater module as described in Patent Document 1 has been known, for example.
The thin heater module described in Patent Document 1 has a heater main body located adjacent to an outer surface of a battery pack case which has a large number of battery modules housed therein. A heat insulation sheet is interposed between the heater main body and a heater unit case opposed to the heater main body.